The invention of the present application concerns a method of removing phosphoric acid from general domestic wastewater, industrial wastewater or the like. Further, more in particular, the invention of the present application concerns a method of removing phosphoric acid from domestic wastewater, as well as various kinds of wastewater discharged from food industries to and agricultural production fields.
The concentration of phosphoric acid in domestic wastewater is about 2 to 3 mg/L and removal of phosphoric acid in the domestic wastewater has become an important subject for the requirement of removing phosphoric acid from wastewater, for example, from food industries and agricultural production fields, as well as for preventing eutrophication rivers and lakes.
In view of the subject described above, studies have been made so far on the removal of phosphoric acid. Then, a method of removing phosphoric acid by reacting phosphoric acid in a solution containing calcium in excess has been proposed. However, since this existent method is adapted to add a calcium solution to liquid wastes containing phosphoric acid by way of a pump or the like, it has been a problem that calcium can not easily be added in domestic wastewater draining channels.
In view of the above, for solving the subject in the prior art as described above and facilitating addition of calcium to wastewater, the inventors of the present application have invented a method of gradually releasing calcium by supports including calcium and adding the same to wastewater in draining channels.
That is, the invention provides, at first, a method of removing phosphoric acid contained in wastewater, which comprises including and immobilizing calcium or a compound thereof in a polymeric solid, bringing the same into contact with wastewater and forming calcium apatite by the reaction between phosphoric acid in wastewater and calcium.
Further, the invention provides, secondly, a method of removing phosphoric acid contained in wastewater, which comprises including and immobilizing calcium or a compound thereof and magnetite in a polymeric solid, bringing the same into contact with wastewater and forming calcium apatite by the reaction between phosphoric acid in wastewater and calcium.
The invention provides, thirdly, the method described above in which the calcium compound is at least one member from water solubilized calcium, inorganic acid salt of calcium and organic carboxylic acid salt of calcium, fourthly, the method as described above in which the polymeric solid is at least one member from polyvinyl alcohol, partially esterified polyvinyl alcohol, polyacrylic acid, partially esterified polyacrylic acid, starch, partial acetylated starch, polysaccharides and partial esterified product of polysaccharides, fifthly, the method as described above in which the polymeric solid is a gelled polyvinyl alcohol or a partially esterified product thereof, sixthly, the method as defined above in which the polymeric solid has a multi-layered structure and, seventhly, the method described above in which the polymeric solid is formed with a coating layer of calcium alginate.
Then, the invention provides, eighthly, a method of controlling surface deposition of calcium phosphate and diffusion of calcium by mechanically vibrating a polymeric solid containing calcium or a compound thereof, ninthly, a method of controlling surface deposition of calcium phosphate and diffusion of calcium by mechanically or electromagnetically vibrating a polymeric solid containing calcium or a compound thereof and magnetite, and, tenthly, a method of recovering calcium apatite formed in running water.
Further, the invention provides, eleventhly, an inclusive immobilizing support for removing phosphoric acid in wastewater in which calcium or a compound thereof is supported on a polymeric solid, and, twelfthly, an inclusion immobilizing support in which magnetite is contained in the polymeric solid.